Recent advances in molecular biology have resulted in a range of novel experimental and potentially therapeutic tools becoming more widely available. Manipulation of the mammalian genome has been possible only since the late 1980s, and lines of animals are now routinely developed that have either targeted disruption or overexpression of a particular gene. These animals enable investigation of the mechanisms of normal growth and development, as well as of disease processes, hopefully leading to the development of more specific and innovative therapies and possibly therapeutic genetic manipulation.
Currently, I am undertaking a period of research at the Victor Chang Cardiac Research Institute in Sydney, Australia, which is part of St Vincents Hospital and affiliated with the University of New South Wales. The main project is an investigation into the use of genetic manipulation of skeletal muscle for use in cardiac assistance. The most obvious example of such cardiac assistance is cardiomyoplasty, but it encompasses other procedures such as aortomyoplasty, skeletal muscle ventricles, myoblast transplantation and mechanical devices powered by skeletal muscle, which are currently under active investigation worldwide. All of these procedures are limited to varying extents by the inherent differences between skeletal and cardiac muscle and the changes that occur on mobilisation and electrical transformation. The aim is to address these issues utilizing a genetic approach, effectively reprogramming the muscle of interest and altering its phenotype to one more suited to its new function. Attributes such as hypertrophy, vascularity and fibre type are all particularly amenable to manipulation by appropriately targeted gene therapies. A range of issues are being investigated - what genes to use, what controllers (enhancer and promoter elements) to link them to, and, a major issue in all gene therapy, how to optimise delivery to the tissue of interest. The final step, of course, will be an assessment of the effect of the transformation on overall muscle function. The effects of this manipulation are also under examination at the molecular level, and new insights into the normal pathways of muscle development and hypertrophy have been obtained. Interestingly, the majority of our findings are also applicable to cardiac muscle, thus opening the possibility of using these approaches in the diseased heart.
Other interests of the Institute include the molecular mechanisms of cardiac hypertrophy, failure and development. The tools of targeted gene disruption and overexpression have been used to develop several animal lines that model a range of cardiac disorders, and thus provide a tool to study these disorders in more detail. Unfortunately, for a wide range of technical and economical reasons, the animals thus developed are all mice. This leads to the other main aspect of my work here - developing a range of methods to accurately assess the cardiac physiology of these models. The size limitation is the most obvious problem - the animals are 20 to 30 grams, with hearts weighing 100-150mg and resting heart rates of approximately 500bpm. However, their physiological, as well as genetic, make-up has significant similarities to larger mammals, giving such studies validity and relevance to human conditions. Advances in engineering have enabled the development of a range of devices suitable for the instrumentation of these animals. As part of the protocol developed for their phenotypic assessment, we can now routinely obtain an ECG, cannulate the left ventricle retrogradely through the carotid artery (enabling pressure measurements and indices of contractility and relaxation), perform M-mode and 2D echocardiography and are now using epicardial microcrystals to enable pressure-volume loops to be derived. At its most invasive, the procedure may entail an anesthetised, ventilated mouse attached to an ECG monitor, with both jugulars cannulated, a pressure transducer in the LV and chest open with epicardial crystals around the heart! The animals are actually stable in this manner for over an hour, enabling a range of experiments to be performed.
So what are the advantages of surgical involvement in this sort of molecular/genetic research? In fact, both parties gain. The phenotypic assessment of disease models is a typical example where an interdisciplinary approach is vital to fully evaluate the physiological and pathological effects of the genetic alteration and determine its relevance to the human condition. There is an increasing amount of genetically oriented research appearing in surgical and medical journals, as well as those aimed at basic scientists, and familiarity with the techniques described greatly facilitates the interpretation of this work. A mutual advantage is in the identification of directions for future research as basic scientists learn what problems we face, and we become aware of the techniques and knowledge available, the two areas can come together more productively. The support of the Society through the St Jude Scholarship is much appreciated as the funding for clinicians to undertake this kind of research abroad becomes increasingly scarce.